[devhelp] Sidebar: add missing (nullable) annotation

[Sébastien Wilmet <swilmet src gnome org>]

commit 9c60511d3976dbd9254356ea8cadfe3fd7ad9027
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sat May 13 14:06:55 2017 +0200

    Sidebar: add missing (nullable) annotation

 src/dh-sidebar.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/dh-sidebar.c b/src/dh-sidebar.c
index 80c459c..9e6060c 100644
--- a/src/dh-sidebar.c
+++ b/src/dh-sidebar.c
@@ -500,8 +500,8 @@ dh_sidebar_select_uri (DhSidebar   *sidebar,
 
 /**
  * dh_sidebar_new:
- * @book_manager: a #DhBookManager. This parameter is deprecated, you can just
- * pass %NULL.
+ * @book_manager: (nullable): a #DhBookManager. This parameter is deprecated,
+ * you should just pass %NULL.
  *
  * Returns: (transfer floating): a new #DhSidebar widget.
  */